The Lymphatic System and Immunity

Parts of the Lymphatic System The lymphatic system includes a wide variety of cells, vessels, glands, and organs that aid with fluid movement and immunity in the body.

Lymphatic Fluid Lymphatic vessels transport lymph (similar to plasma) from body tissues into the veins. Transport excess fluid out of tissue and into veins.

Lymphocytes are a class of white blood cell (leukocyte) that provide specialized protection against pathogens such as bacteria, viruses, fungi, and parasites.

Lymph nodes are located along lymphatic pathways. Contain high concentrations of lymphocytes and macrophages.

The tonsils are a visible set of lymph nodes at the back of the oral cavity.

The thymus gland, is a lymphatic organ that helps to produce lymphocytes. The spleen also helps to produce lymphocytes, in addition to filtering microbes and worn red blood cells.

Nonspecific Defenses Mechanical barriers prevent the entrance of infectious agents. Epidermis Mucous membranes in the respiratory tract. Hair Chemical barriers include any substance that reacts with and damages pathogens. Acidic body secretions (stomach acid, urine). Exocrine enzymes (lysozyme in tears) Salt from sweat.

Lymphocytes can secrete a hormone-like peptide called interferon which will stimulate cells to produce defensive proteins that block virus replication. Complement is a group of proteins found in plasma that stimulates inflammation and attracts phagocytes.

Phagocytes remove any foreign particles or microorganisms in the blood stream. Phagocytosis is also known as “cellular eating.”

Pus is a thick fluid that contains dead phagocytes, white blood cells, and damaged tissue.

There are two types of phagocytes in the bloodstream: Neutrophils are able to leave the blood stream and phagocytize cell debris or invading bacteria in infected tissue. Eosinophils play an important role in fighting parasitic infections and during allergic reactions.

Natural killer (NK) cells specifically attack cells infected by viruses or that have become cancerous. Secrete a substance called perforin that breaks apart the cell membrane, killing the cell.

Specific Immunity Specific immunity involves a response of leukocytes that target one type of antigen. Antigens are proteins, polysaccharides, or glycoproteins located on the surface of a cell. The immune system recognizes these antigens as “self” or “nonself”.

Two lymphocytes are involved in specific immunity: Locations of cell production: B cells: Produced in bone marrow. T cells: Produced in the thymus.

Lymphocyte Activation Lymphocytes must be activated before they can respond to an antigen. They are called antigen- presenting cells. Macrophages engulf bacteria and viruses and use their lysosomes to digest them. They are able to present the antigens on its cell membrane.

The first lymphocyte to be activated is the Helper T cell. The Helper T cell begins to divide and proliferate rapidly. Helper T Cells are a class of protein molecules called cytokines are released, which activates two other lymphocytes that have also combined with the same antigen: Cytotoxic T cells B cells

The activated B-cells also begin to divide and proliferate Interleukin are a group of cytokines that were first seen to be expressed by white blood cells (leukocytes). The activated B-cells also begin to divide and proliferate These B-cells become plasma cells, which secrete proteins called antibodies. Antibodies correspond with the shape of the antigen of the bacteria or virus.

The antibodies begin sticking to the surface of the virus or bacteria. This effectively disables the pathogen, rendering it unable to invade other tissues. The pathogen is more easily caught and phagocytized by macrophages.

The activated Cytotoxic T-cells begin searching for infected cells, which they can destroy with a special protein called perforin. Perforin causes holes to be produced throughout the cell membrane, causing the cell to burst.

Following the primary immune response, a few memory cells of the Cytotoxic T cells and B cells will remain and circulate through the blood. Allows for a much more rapid secondary immune response should the specific bacteria or virus return.

Primary Immune Response

Secondary Immune Response

Immune Deficiency The Human Immunodeficiency Virus, or HIV, specifically infects and destroys Helper T cells. This renders the immune system unable to signal B cells to produce antibodies or cytotoxic T cells to kill infected cells. Patients with AIDS are thus highly susceptible to secondary opportunistic infection.

https://www.youtube.com/watch?v=9yP3IUcCP W4

Allergic Reactions An allergic reaction is a response to a nonharmful substance. The causes of allergies vary and are not fully understood. Delayed-reaction allergies involve the repeated activation of antigen-presenting cells against a harmless substances, which triggers an immune reaction and eventually, memory cells. Immediate-reaction allergies are an inherited tendency to produce antibodies in response to certain allergens. https://www.youtube.com/watch?v=ZmXm80BSfPU

Autoimmunity If the immune system becomes unable to distinguish self from non-self antigens, it results in an autoimmune disorder.